Bioabsorbable resin for additive manufacturing

ABSTRACT

Provided herein according to aspects of the present invention are resins that: (a) are suitable for use in additive manufacturing techniques such as bottom-up and top-down stereolithography, (b) produce objects that are bioresorbable, and (c) produce objects that are flexible or elastic (preferably at at least typical room temperatures of 25° C., and in some embodiments at typical human body temperatures of 37° C.). Such resins may include: (a) a bioresorbable polyester oligomer having reactive end groups; (b) non-reactive diluent; (c) optionally reactive diluent; and (d) a photoinitiator.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/753,415, filed Mar. 2, 2022, which is a 35 U.S.C. § 371 nationalphase application of International Application Serial No.PCT/US2020/051047, filed Sep. 16, 2020, which claims priority from andthe benefit of U.S. Provisional Application Ser. Nos. 62/900,708,62/913,227, and 63/073,021, filed Sep. 16, 2019, Oct. 10, 2019, and Sep.1, 2020, respectively, the disclosures of which are hereby incorporatedherein in their entireties.

BACKGROUND

Resins for the production of bioresorbable objects are known anddescribed in, for example, U.S. Pat. Nos. 9,770,241; 10,085,745;10,149,753; and 9,873,790; and in US Patent App. Pub. No. 2017/0355815.However, not all such resins are well-suited for use in additivemanufacturing techniques such as stereolithography due to the sometimescompeting needs for (a) printability in the additive manufacturingprocess (e.g., sufficiently low viscosity), (b) flexible or elasticmechanical properties in the object produced, and (c) reasonablebioabsorption/biodegradation times.

In one prior work, a polycaprolactone dimethacrylate based resin wasinvestigated for printing a bioresorbable porous scaffold withstereolithography (Elomaa et al., Preparation ofpoly(e-caprolactone)-based tissue engineering scaffolds bystereolithography, Acta Biomaterialia 7, 3850-3856 (2011)). Although themechanical properties of Elomaa et al.'s resin are useful for someimplantable objects, their degradation time (generally greater than 2years) is slower than preferred.

In another prior reference, a poly(D,L-lactide) dimethacrylate basedresin was investigated (Melchels et al., Effects of the architecture oftissue engineering scaffolds on cell seeding and culturing, ActaBiomaterialia 6 4208-4217 (2010)). However, the Melchels et al. curedresin is rigid and non-elastic, which is less preferred for productionof some implantable (or other biomedical) objects that undergo largeelastic deformation during implant and/or use.

Accordingly, there remains a need for new additive manufacturing resinssuitable for biomedical applications.

SUMMARY

A first aspect of the present disclosure is a resin useful for producingobjects. The resins (a) are suitable for use in additive manufacturingtechniques such as bottom-up and top-down stereolithography, (b) produceobjects that are bioresorbable, and (c) produce objects that areflexible or elastic (preferably at at least typical room temperatures of25° C., and in some embodiments at typical human body temperatures of37° C.). Such resins typically include: (a) a bioresorbable polyesteroligomer having reactive end groups; (b) non-reactive diluent; (c)optionally reactive diluent; and (d) a photoinitiator.

In some aspects, the resin comprises or consists essentially of: (a)from 5 or 10 percent by weight to 80 or 90 percent by weight of(meth)acrylate terminated bioresorbable polyester oligomer; (b) from 1or 5 percent by weight to 50 or 70 percent by weight of non-reactivediluent; (c) from 0.1 or 0.2 percent by weight to 2 or 4 percent byweight of photoinitiator; (d) optionally, from 1 or 5 percent by weightto 40 or 50 percent by weight of reactive diluent; (e) optionally, from1 or 2 percent by weight to 40 or 50 percent by weight of filler; and(f) optionally, from 1 or 2 percent by weight to 5 or 10 percent byweight of at least one additional cross-linking agent, such astrimethylolpropane trimethacrylate (TMPTMA).

In some aspects, the oligomer may include a linear oligomer and/or abranched oligomer (i.e., a star oligomer, such as a tri-arm oligomer).

The oligomer according to some aspects may comprise degradable esterlinkages between constituents selected from caprolactone, lactide,glycolide, trimethylene carbonate, dioxanone, and propylene fumaratemonomers in an ABA block, BAB block, CBC block, BCB block, AB randomcomposition, BC random composition, homopolymer, or any combinationthereof, wherein: A=poly(lactide) (PLA), poly(glycolide) (PGA),poly(lactide-co-glycolide) (PLGA), or polypropylene fumarate (PPF),B=polycaprolactone (PCL), polytrimethylene carbonate (PTMC), orpoly(caprolactone-co-lactide) (PCLLA), and C=polydioxanone (PDX).

In some aspects the oligomer has a molecular weight of from 2 or 5kilodaltons to 6, 10, 15 or 20 kilodaltons.

In some aspects the oligomer comprises an ABA block, a BAB block, a CBCblock, or a BCB block in linear and/or branched (e.g., star or tri-arm)form.

In some aspects A is: (i) poly(lactide); (ii) poly(glycolide); (iii)poly(lactide-co-glycolide) containing lactide and glycolide in a molarratio of (i) from 90:10 to 55:45 lactide:glycolide (i.e., a lactide richratio) or (ii) from 45:55 to 10:90 lactide:glycolide (i.e., a glycoliderich ratio); or any combination of the foregoing.

In some aspects B is: (i) polycaprolactone; (ii) polytrimethylenecarbonate; (iii) poly(caprolactone-co-lactide) containing caprolactoneand lactide in a molar ratio of 95:5 to 5:95 caprolactone:lactide; orany combination of the foregoing.

In some aspects A (PLA, PGA, PLGA, PPF, or a combination thereof) has amolecular weight of from 1,000 or 2,000 daltons, up to 4,000, 6,000 or10,000 daltons; and/or B (PCL, PTMC, PCLLA, or a combination thereof)has a molecular weight (Mn) of from 1,000 or 1,600 daltons, up to 4,000,6,000 or 10,000 daltons.

In some aspects the non-reactive diluent is selected from the groupconsisting of dimethylformamide, dimethylacetamide, N-methyl pyrrolidone(NMP), dimethyl sulfoxide, cyclic carbonate (such as propylenecarbonate), diethyl adipate, methyl ether ketone, ethyl alcohol,acetone, and combinations thereof. In some aspects the non-reactivediluent is propylene carbonate.

In some aspects the reactive diluent comprises an acrylate, amethacrylate, a styrene, a vinylamide, a vinyl ether, a vinyl ester,polymers containing any one or more of the foregoing, or a combinationof two or more of the foregoing.

In some aspects the resin further includes at least one additionalingredient selected from: pigments, dyes, active compounds orpharmaceutical compounds, and detectable compounds (e.g., fluorescent,phosphorescent, radioactive), and combinations thereof.

In some aspects the resin further includes a filler (e.g., bioresorbablepolyester particles, sodium chloride particles, calcium triphosphateparticles, sugar particles).

In some aspects the resin consists essentially of: (a) from 5 or 10percent by weight to 80 or 90 percent by weight of a (meth)acrylateterminated, linear or branched, bioresorbable polyester oligomer ofmonomers in an ABA block, a BAB block, a CBC block, or a BCB block,wherein: A is poly(lactide) (PLA), poly(glycolide) (PGA),poly(lactide-co-glycolide) (PLGA), or a combination thereof, with saidPLGA containing lactide and glycolide in a molar ratio of either 90:10to 60:40 lactide:glycolide (i.e., a lactide rich ratio) or 40:60 to10:90 lactide:glycolide (i.e., a glycolide rich ratio), and A has amolecular weight (Mn) of from 1,000 or 2,000 daltons, up to 4,000 or10,000 daltons); B is polycaprolactone (PCL, PTMC, PCLLA) and has amolecular weight (Mn) of from 1,000 or 1,600 daltons, up to 4,000 or10,000 daltons; and C is polydioxanone (PDX) and has a molecular weight(Mn) of from 1,000 or 2,000 daltons, up to 4,000 or 10,000 daltons) and(b) from 1 or 5 percent by weight to 50 or 70 percent by weight ofpropylene carbonate; (c) from 0.1 or 0.2 percent by weight to 2 or 4percent by weight of photoinitiator, (d) optionally, from 1 or 5 percentby weight to 40 or 50 percent by weight of reactive diluent; and (e)optionally, from 1 or 2 percent by weight to 40 or 50 percent by weightof filler.

In some aspects the resin consists essentially of: (a) from 10 percentby weight to 80 percent by weight of (meth)acrylate terminated,bioresorbable, branched polyester oligomer; wherein said branchedoligomer comprises degradable ester linkages between constituents in anABA block, BAB block, or AB random composition, where A is poly(lactide)or poly(lactide-co-glycolide), B is polycaprolactone orpoly(caprolactone-co-lactide), and said oligomer has a molecular weight(Mn) of from 2 to 6 kilodaltons; (b) from 5 percent by weight to 50percent by weight of non-reactive diluent selected from the groupconsisting of N-methyl pyrrolidone (NMP) and propylene carbonate; (c)from 0.2 percent by weight to 2 percent by weight of photoinitiator; (d)optionally, from 1 percent by weight to 50 percent by weight of reactivediluent; (e) optionally, from 1 percent by weight to 50 percent byweight of filler; and (f) optionally, from 1 percent by weight to 10percent by weight of additional crosslinking agent.

Also provided is a method of making a flexible or elastic bioresorbableobject, comprising producing said object by photopolymerizing a resin astaught herein in the shape of the object (e.g., by additivemanufacturing, such as by bottom-up or top-down additive manufacturing).

In some aspects the method further comprises cleaning said object (e.g.,by washing, wiping, spinning, etc.) after said producing step (butpreferably before said step of exposing said object to additionallight).

In some aspects the method further comprises exposing said object toadditional light after said producing step to further reactunpolymerized constituents therein.

In some aspects the method further comprises extracting residual diluentfrom said object after said producing step.

In some aspects the method further comprises drying said object(optionally but preferably under a vacuum) to remove extraction solventstherefrom.

In some aspects the method further comprises producing said object inenlarged form to offset shrinkage of said object that occurs during saidextracting, further exposing, and/or cleaning steps, and drying steps.

Also provided is a flexible or elastic bioresorbable object produced bya method as taught herein.

Additional aspects of the present invention are explained in greaterdetail below.

DETAILED DESCRIPTION

The present invention is now described more fully hereinafter. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein; rather,these embodiments are provided so that this disclosure will be thoroughand complete and will fully convey the scope of the invention to thoseskilled in the art.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises” or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements components and/orgroups or combinations thereof, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components and/or groups or combinations thereof.

As used herein, the term “and/or” includes any and all possiblecombinations of one or more of the associated listed items, as well asthe lack of combinations when interpreted in the alternative (“or”).

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly-useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the specification andclaims and should not be interpreted in an idealized or overly formalsense unless expressly so defined herein. Well-known functions orconstructions may not be described in detail for brevity and/or clarity.

The transitional phrase “consisting essentially of” means that the scopeof a claim is to be interpreted to encompass the specified materials orsteps recited, and also additional materials or steps that do notmaterially affect the basic and novel characteristics of the claimedinvention as described herein.

The disclosures of all patent references cited herein are to beincorporated herein by reference in their entirety.

1. Polymer Materials and Resins.

Resins useful for carrying out the present invention generally comprise,consist of, or consist essentially of:

(a) from 5 or 10 percent by weight to 80 or 90 percent by weight of(meth)acrylate terminated bioresorbable polyester oligomer;

(b) from 1 or 5 percent by weight to 50 or 70 percent by weight ofnon-reactive diluent;

(c) from 0.1 or 0.2 percent by weight to 2 or 4 percent by weight ofphotoinitiator;

(d) optionally, from 1 or 5 percent by weight to 40 or 50 percent byweight of reactive diluent;

(e) optionally, from 1 or 2 percent by weight to 40 or 50 percent byweight of filler; and

(f) optionally, from 0.1 or 1 percent by weight to 10 or 20 percent byweight of additional ingredients such as an active agent, detectablegroup, pigment or dye, or the like.

Oligomer prepolymers for resins from which the polymers may be producedmay be linear or branched (e.g., “star” oligomers such as tri-armoligomers). Suitable end groups for such monomers or oligomerprepolymers include, but are not limited to, acrylate, methacrylate,fumarate, vinyl carbonate, methylester, ethylester, etc. Non-limitingexamples of suitable resin compositions are given in Table 1 below(where constituents in each column can be combined with constituents ofthe other columns in any combination).

TABLE 1 Backbone Reactive Oligomer Chemistry End Group ArchitecturePlasticizer Diluent Photo-initiator PLGA Methacrylate Linear HO-PCL-OHMono-vinyl Irgacure ® ether 2959 PCL Acrylate Star HO-PLGA- DEGMAIrgacure ® (branching) PCL-PLGA- TPO OH PLGA-PCL- Vinyl Vinyl acetateITX PLGA Carbonate PLGA-PEG- Fatty acid n-butyl Irgacure ® PLGA methylester methacrylate 819 PLGA-PCL Triacetine NMP DMSO divinyl adipate PLGA= poly(lactic-co-glycolic acid); PEG = polyethylene glycol;PCL=polycaprolactone; DEGMA = Di(ethylene glycol) methyl ethermethacrylate; TPO = diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide;ITX = isopropylthioxanthone; NMP = N-methyl pyrrolidone; DMSO =dimethylsulfoxide.

A particular example of a composition for use in producing the objectsdescribed herein is based on a methacrylate terminated oligomer with abioresorbable polyester linkage, which provides rubber-like elasticbehavior at physiological temperatures, short-term retention ofmechanical properties (in some embodiments, 1 month or less), andlong-term full resorption (in some embodiments, over a time ofapproximately 4-6 months).

Bioresorbable polyester oligomers for use in some preferred embodimentsare, in general, bioresorbable oligomers with methacrylate end-groups.Such oligomers are typically comprised of degradable ester linkagesselected from caprolactone, lactide, glycolide, trimethylene carbonate,dioxanone, and propylene fumarate monomers in an ABA block, BAB block,CBC block, BCB block, AB random composition, BC random composition,homopolymer, or any combination thereof, where: A=poly(lactide) (PLA),poly(glycolide) (PGA), or poly(lactide-co-glycolide) (PLGA),polypropylene fumarate (PPF), B=polycaprolactone (PCL), polytrimethylenecarbonate (PTMC), poly(caprolactone-co-lactide) (PCLLA) andC=polydioxanone (PDX). Copolymers may have a molecular weight (Mn) offrom 2 or 5 kilodaltons to 6, 10, 15 or 20 kilodaltons, in either linearor star structure. Monomers used to produce such oligomers mayoptionally introduce branches, such as to enhance elasticity, as isknown in the art, an example being gamma-methyl-epsilon caprolactone andgamma-ethyl-epsilon-caprolactone.

Lactides may be L-Lactides, D-Lactide, or mixtures thereof (i.e.,D,L-Lactides). For PLA blocks, it is in some embodiments preferred touse L-Lactide, for better regularity and higher crystallinity.

In some embodiments, the oligomer comprises an ABA block, a BAB block, aCBC block, or a BCB block in linear and/or branched (e.g., star ortri-arm) form.

In some embodiments, A is: (i) poly(lactide); (ii) poly(glycolide);(iii) poly(lactide-co-glycolide) containing lactide and glycolide in amolar ratio of either 90:10 to 55:45 lactide:glycolide (i.e., a lactiderich ratio) or 45:55 to 10:90 lactide:glycolide (i.e., a glycolide richratio); or any combination thereof. In some embodiments, A D,L-Lactidemixture can be used for making the PLGA random copolymer.

In some embodiments, A (PLA, PGA, PLGA, PPF, or a combination thereof)has a molecular weight (Mn) of from 1,000 or 2,000 daltons, up to 4,000or 10,000 daltons); and B (PCL, PTMC, and PCLLA) has a molecular weight(Mn) of from 1,000 or 1,600 daltons, up to 4,000 or 10,000 daltons.

In some embodiments, at least one additional cross-linking agent can beincluded (e.g., in an amount of from 1 or 2 percent by weight to 5 or 10percent by weight). Any suitable additional cross-linking agents can beused, including bioabsorbable crosslinking agents, non-absorbablecrosslinking agents, and combinations thereof. Examples of suitablebioabsorbable crosslinking agents include, but are not limited to,divinyl adipate (DVA), poly(caprolactone)trimethacrylate (PCLDMA, e.g.,at a molecular weight Mn of about 950 to 2400 daltons), etc. Examples ofsuitable non-absorbable crosslinking agents include, but are not limitedto, trimethylolpropane trimethacrylate (TMPTMA), poly(propylene glycol)dimethacrylate (PPGDMA), poly(ethylene glycol) dimethacrylate (PEGDMA),etc.

A particular embodiment is a resin consisting essentially of: (a) from 5or 10 percent by weight to 80 or 90 percent by weight of a(meth)acrylate terminated, linear or branched, bioresorbable polyesteroligomer of monomers in an ABA block, a BAB block, a CBC block, or a BCBblock, wherein: A is poly(lactide) (PLA), poly(glycolide) (PGA),poly(lactide-co-glycolide) (PLGA), or a combination thereof, with saidPLGA containing lactide and glycolide in a molar ratio of either 90:10to 60:40 lactide:glycolide (i.e., a lactide rich ratio) or 40:60 to10:90 lactide:glycolide (i.e., a glycolide rich ratio), and A has amolecular weight (Mn) of from 1,000 or 2,000 daltons, up to 4,000 or10,000 daltons; B is polycaprolactone (PCL, PTMC, and PCLLA) and has amolecular weight (Mn) of from 1,000 or 1,600 daltons, up to 4,000 or10,000 daltons; and C is polydioxanone (PDX) and has a molecular weight(Mn) of from 1,000 or 2,000 daltons, up to 4,000 or 10,000 daltons; (b)from 1 or 5 percent by weight to 50 or 70 percent by weight of propylenecarbonate; (c) from 0.1 or 0.2 percent by weight to 2 or 4 percent byweight of photoinitiator, (d) optionally, from 1 or 5 percent by weightto 40 or 50 percent by weight of reactive diluent; and (e) optionally,from 1 or 2 percent by weight to 40 or 50 percent by weight of filler.

Non-reactive diluents that can be used in carrying out the inventioninclude, but are not limited to, dimethylformamide, dimethylacetamide,N-methyl pyrrolidone (NMP), dimethyl sulfoxide, cyclic carbonate (forexample, propylene carbonate), diethyl adipate, methyl ether ketone,ethyl alcohol, acetone, and combinations of two or more thereof.

Photoinitiators included in the polymerizable liquid (resin) can be anysuitable photoiniator, including type I and type II photoinitiators andincluding commonly used UV photoinitiators, examples of which includebut are not limited to acetophenones (diethoxyacetophenone for example),phosphine oxides such as diphenyl(2,4,6-trimethylbenzoyl)phosphineoxide, phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (PPO),Irgacure® 369, etc. See, e.g., U.S. Pat. No. 9,453,142 to Rolland et al.

Reactive diluents (including di and tri-functional reactive diluents)that can be used in carrying out the invention can include an acrylate,a methacrylate, a styrene, a vinylamide, a vinyl ether, a vinyl ester,polymers containing any one or more of the foregoing, and combinationsof one or more of the foregoing (e.g., acrylonitrile, styrene, divinylbenzene, vinyl toluene, methyl acrylate, ethyl acrylate, butyl acrylate,methyl (meth)acrylate, isobornyl acrylate (IBOA), isobornyl methacrylate(IBOMA), an alkyl ether of mono-, di- or triethylene glycol acrylate ormethacrylate, a fatty alcohol acrylate or methacrylate such as lauryl(meth)acrylate, and mixtures thereof).

The resin can have additional ingredients therein, including pigments,dyes, diluents, active compounds or pharmaceutical compounds, detectablecompounds (e.g., fluorescent, phosphorescent, radioactive), etc., againdepending upon the particular purpose of the product being fabricated.Examples of such additional ingredients include, but are not limited to,proteins, peptides, nucleic acids (DNA, RNA) such as siRNA, sugars,small organic compounds (drugs and drug-like compounds), etc., includingcombinations thereof.

Fillers. Any suitable filler may be used in connection with the presentinvention, including but not limited to bioresorbable polyesterparticles, sodium chloride particles, calcium triphosphate particles,sugar particles, etc.

Dyes/non-reactive light absorbers. In some embodiments, resins forcarrying out the present invention include a non-reactive pigment or dyethat absorbs light, particularly UV light. Suitable examples of suchlight absorbers include, but are not limited to: (i) titanium dioxide(e.g., included in an amount of from 0.05 or 0.1 to 1 or 5 percent byweight), (ii) carbon black (e.g., included in an amount of from 0.05 or0.1 to 1 or 5 percent by weight), and/or (iii) an organic ultravioletlight absorber such as a hydroxybenzophenone,hydroxyphenylbenzotriazole, oxanilide, benzophenone, thioxanthone,hydroxyphenyltriazine, and/or benzotriazole ultraviolet light absorber(e.g., Mayzo BLS1326) (e.g., included in an amount of 0.001 or 0.005 to1, 2 or 4 percent by weight). Examples of suitable organic ultravioletlight absorbers include, but are not limited to, those described in U.S.Pat. Nos. 3,213,058; 6,916,867; 7,157,586; and 7,695,643, thedisclosures of which are incorporated herein by reference.

2. Methods of Making.

Additive manufacturing. Suitable additive manufacturing apparatus andmethods on which objects can be produced include bottom-up and top-downadditive manufacturing methods and apparatus, as known and described in,for example, U.S. Pat. No. 5,236,637 to Hull, U.S. Pat. Nos. 5,391,072and 5,529,473 to Lawton, U.S. Pat. No. 7,438,846 to John, U.S. Pat. No.7,892,474 to Shkolnik, U.S. Pat. No. 8,110,135 to El-Siblani, U.S.Patent Application Publication No. 2013/0292862 to Joyce, and US PatentApplication Publication No. 2013/0295212 to Chen et al. The disclosuresof these patents and applications are incorporated by reference hereinin their entirety.

In some embodiments, the additive manufacturing step is carried out byone of the family of methods sometimes referred to as continuous liquidinterface production (CLIP). CLIP is known and described in, forexample, U.S. Pat. Nos. 9,211,678; 9,205,601; 9,216,546; and others; inJ. Tumbleston et al., Continuous liquid interface production of 3DObjects, Science 347, 1349-1352 (2015); and in R. Janusziewcz et al.,Layerless fabrication with continuous liquid interface production, Proc.Natl. Acad. Sci. USA 113, 11703-11708 (2016). Other examples of methodsand apparatus for carrying out particular embodiments of CLIP include,but are not limited to: Batchelder et al., US Patent Application Pub.No. US 2017/0129169; Sun and Lichkus, US Patent Application Pub. No. US2016/0288376; Willis et al., US Patent Application Pub. No. US2015/0360419; Lin et al., US Patent Application Pub. No. US2015/0331402; D. Castanon, S Patent Application Pub. No. US2017/0129167. B. Feller, US Pat App. Pub. No. US 2018/0243976; M. Panzerand J. Tumbleston, US Pat App Pub. No. US 2018/0126630; and K. Willisand B. Adzima, US Pat App Pub. No. US 2018/0290374.

Post-production steps. After the additive manufacturing steps,additional post processing steps can include washing (e.g., in anorganic solvent such as acetone, isopropanol, a glycol ether such asdipropylene glycol methyl ether or DPM), wiping (e.g., with an absorbentmaterial, blowing with a compressed gas or air blade, etc.) centrifugalseparation of residual resin, extraction of residual solvents,additional curing such as by flood exposure with ultraviolet light orthe like, drying said object (optionally but preferably under a vacuum)to remove extraction solvents therefrom, and combinations of some or allof the foregoing, in accordance with known techniques.

3. Utility.

Resins as described herein are useful for making a variety of biomedicaldevices and medical aids, including implantable devices such asintravascular stents. Additional examples of objects that can be madewith the resins described herein include, but are not limited to, thoseset forth in Williams et al., Surgical Mesh Implants containingpoly(butylene succinate) and copolymers thereof, US Patent ApplicationPub. No. 2019/0269817, (Sep. 5, 2019) and in Hartwell et al.,Collapsible dressing for negative pressure wound treatment, US PatentApplication Pub. No. 2019/0240385 (Aug. 8, 2019), the disclosures ofwhich are incorporated by reference herein in their entirety.

The present invention is explained in greater detail in the followingnon-limiting Examples.

Examples 1-3 Preparation of a Difunctional Methacrylate (MA) TerminatedPolyester Oligomer

These examples describe the preparation of a difunctional, methacrylateterminated, polyester oligomer. The midblock is PLGA-PCL-PLGA, themolecular weight is 6 kilodaltons, and PCL is included as 40 wt % of thetotal MW. PLGA is a random copolymer of lactide (L) and glycolide (G)with an L:G weight ratio of 1:1.

Refer to Table 2 for an example of the molar ratios and masses of eachreagent used for a 1 kg batch of HO-PLGA-b-PCL-b-PLGA-OH synthesis asthe next two sections are discussed.

TABLE 2 Example of molar ratios and mass of each reagent needed tosynthesize a 1 kg batch of HO-PLGA-b-PCL-b-PLGA-OH. Molecular WeightMolar Density Mass Volume Reagent (g/mol) Ratio (g/mol) (g) (mL) MolesCaprolactone (CL) 114.14 22 1.03 400.0 388.4 3.50 Diethylene glycol106.12 1 1.12 16.9 15.1 0.16 (DEG) Stannous Octoate 405.12 2.38 × 10⁻³1.25 0.15 0.12 3.8 × 10⁻⁴ (Sn(Oct)) D,L-Lactide (L) 144.13 14 — 321.4 —2.22 Glycolide (G) 116.07 14 — 258.8 — 2.22

Example 1 HO-PCL-OH Synthesis

A round bottom flask was dried in a drying oven overnight and cooledunder N₂ flow to room temperature. Caprolactone and tin octoate wereadded to the round bottom flask via a glass syringe and syringe needle.The reaction flask contents were heated to 130° C. Meanwhile, diethyleneglycol was heated to 130° C. Once preheated, diethylene glycol was addedto the reaction flask as an initiator and was allowed to react untilcomplete monomer conversion. Monomer conversion was monitored using H¹NMR. The reaction was stopped, and the reaction contents were allowed tocool to room temperature. The HO-PCL-OH was precipitated into cold MeOHfrom chloroform to obtain a white solid. H¹ NMR, DSC, FTIR, and THF GPCwere used to characterize HO-PCL-OH.

Example 2 HO-PLGA-b-PCL-b-PLGA-OH Synthesis

HO-PCL-OH and varying amounts of D,L-lactide and glycolide were addedinto a round-bottom flask under N₂ and heated to 140° C. to melt thereaction contents. After melting, the temperature was reduced to 120° C.and stannous octoate was added. The reaction continued with stirringwhile monitoring the monomer conversion with H¹ NMR and THF GPC. Oncethe reaction reaches the desired molecular weight, reaction contentswere cooled to room temperature, dissolved in chloroform andprecipitated into cold diethyl ether three times. The precipitate wasdried under vacuum.

Example 3 MA-PLGA-b-PCL-b-PLGA-MA Synthesis

Refer to Table 3 for an example of the molar ratio and masses of eachreagent used to synthesize a 1 kg batch of MA-PLGA-b-PCL-b-PLGA-MA.

TABLE 3 Example of molar ratios and mass of each reagent needed tosynthesize a 1 kg batch of MA-PLGA-b-PCL-b-PLGA-MA. Molecular WeightMolar Density Mass Volume Reagent (g/mol) Ratio (g/mol) (g) (mL) MolesHO-PLGA-b-PCL- 6000 1 — 1000 — 0.17 b-PLGA-OH Methacryloyl 104.54 3.81.07 66.2 61.9 0.63 Chloride (MC) Triethylamine 101.19 3.8 0.726 64.188.3 0.63 (TEA) Butylated hydroxy- 220.35 ~400 0.45 toluene (BHT) ppmDichloromethane — 0.2 g/mL — — 5000 — (DCM)

HO-PLGA-b-PCL-b-PLGA-OH was dissolved in anhydrous DCM in a round bottomflask under N₂. Triethylamine and a small amount BHT were added thereaction flask and the reaction flask was cooled to 0° C. in an icewater bath. The reaction flask was equipped with a pressure-equalizingaddition funnel that was charged with methacryloyl chloride. Once thereaction flask reached 0° C., methacryloyl chloride was added dropwiseover 2 hours. The reaction proceeded for 12 h at 0° C. and then 24 h atroom temperature. Once complete, the reaction contents were washed withdistilled water 2 times to remove the triethylamine hydrochloride salts,saturated Na₂CO₃, and dried over magnesium sulfate. The collected anddried DCM layer was dried with rotary evaporation. The final product wascharacterized with THF GPC, H¹ NMR, FTIR, and DSC.

Examples 4-6 Preparation of a Tri-Arm MA Terminated Polyester Oligomer

These examples describe the preparation of a tri-arm, or star shaped,bioresorbable polyester oligomer. Each arm is terminated withmethacrylate. Each arm has a molecular weight of 2 kilodaltons and is ablock copolymer of poly(lactide-r-glycolide) (PLGA) andpoly(caprolactone) (PCL) with PCL being the core of the oligomer. ThePCL is included as 40 wt % of the total MW. The PLGA is a randomcopolymer of lactide (L) and glycolide (G) with L:G weight ratio of 1:1.

Example 4 PCL-3OH Synthesis

Refer to Table 4 for an example of the molar ratios and masses of eachreagent used for a 1 kg batch of (PLGA-b-PCL)-3OH synthesis as the nexttwo sections are discussed.

TABLE 4 Example of molar ratios and mass of each reagent needed tosynthesize a 1 kg batch of (PCL-b-PLGA)-3OH. Molecular Weight MolarDensity Mass Volume Reagent (g/mol) Ratio (g/mol) (g) (mL) MolesCaprolactone (CL) 114.14 22 1.03 400.0 388.4 3.50 Trimethylolpropane134.07 1 1.08 21.4 19.8 0.16 (TMP) Stannous Octoate 405.12 2.38 × 1.250.15 0.12 3.81 × (Sn(Oct)) 10⁻³ 10⁻⁴ D,L-Lactide (L) 144.13 14 — 321.4 —2.22 Glycolide (G) 116.07 14 — 258.8 — 2.22

A round bottom flask was dried in a drying oven overnight and cooledunder N₂ flow to room temperature. Caprolactone and tin octoate wereadded to the round bottom flask via a glass syringe and syringe needle.The reaction flask contents were heated to 130° C. Meanwhile,trimethylolpropane (TMP) was heated to 130° C. Once preheated, TMP wasadded to the reaction flask as an initiator and was allowed to reactuntil complete monomer conversion. Monomer conversion was monitoredusing H¹ NMR. The reaction was stopped, and the reaction contents wereallowed to cool to room temperature. The (PCL)-3OH was precipitated intocold MeOH from chloroform to obtain a white solid. H1 NMR, DSC, FTIR,and THF GPC were used to characterize (PCL)-3OH.

Example 5 (PCL-b-PLGA)-3OH Synthesis

(PCL)-3OH and varying amounts of D,L-lactide and glycolide were addedinto a round-bottom flask under N₂ and heated to 140° C. to melt thereaction contents. After melting, the temperature was reduced to 120° C.and stannous octoate was added. The reaction continued with stirringwhile monitoring the monomer conversion with H¹ NMR and THF GPC. Oncethe reaction reaches the desired molecular weight, reaction contentswere cooled to room temperature, dissolved in chloroform andprecipitated into cold diethyl ether three times. The precipitate wasdried under vacuum.

Example 6 (PCL-b-PLGA)-3MA Synthesis

Refer to Table 5 for an example of the molar ratio and masses of eachreagent used to synthesize a 1 kg batch of (PLGA-b-PCL)-3MA.

(PCL-b-PLGA)-3OH was dissolved in anhydrous DCM in a round bottom flaskunder N2. Triethylamine (TEA) and a 400 ppm BHT were added the reactionflask and the reaction flask was cooled to 0° C. in an ice water bath.The reaction flask was equipped with a pressure-equalizing additionfunnel that was charged with methacryloyl chloride. Once the reactionflask reached 0° C., methacryloyl chloride was added dropwise over 2hours. The reaction proceeded for 12 h at 0° C. and then 24 h at roomtemperature. Once complete, the precipitate was removed via vacuumfiltration. The filtrate was collected and DCM was removed with rotaryevaporation. The resulting viscous oil was dissolved in THF andprecipitated into cold methanol. The precipitate was dissolved in DCMand washed with aqueous HCL (3%, 2 times), saturated aqueous sodiumbicarbonate solution, and saturated aqueous sodium chloride, then driedover magnesium sulfate. The magnesium sulfate was filtered off viavacuum filtration, and the filtrate was collected. DCM was removed viarotary evaporation and the solid product was collected and characterizedwith THF GPC, H1 NMR, FTIR, and DSC.

TABLE 5 Example of molar ratios and mass of each reagent needed tosynthesize a 1 kg batch of (PLGA-b-PCL)-3MA. Molecular Weight MolarDensity Mass Volume Reagent (g/mol) Ratio (g/mol) (g) (mL) Moles(PLGA-b-PCL)-3OH 6000 1 — 1000 — 0.17 Methacryloyl Chloride 104.54 4.81.07 83.6 78.2 0.80 (MC) Triethylamine (TEA) 101.19 4.8 0.726 80.9 111.50.63 Butylated hydroxy- 220.35 ~400 ppm 0.47 toluene (BHT)Dichloromethane — 0.2 g/mL — — 5000 — (DCM)

Example 7 Difunctional Oligomer Resin Formulation

The following ingredients were mixed together in the following weightpercents to provide a light polymerizable resin for additivemanufacturing:

-   -   (1) 66.2% of the difunctional oligomer prepared in Examples 1-3        above;    -   (2) 3.5% trimethylolpropane triacrylate (TMPTMA) reactive        diluent;    -   (3) 28.4% of N-methyl pyrrolidone (NMP) non-reactive diluent;        and    -   (4) 1.89% of Irgacure® 819 photoinitiator.

Example 8 Tri-Arm Oligomer Resin Formulation

The following ingredients were mixed together in the following weightpercents to provide a light polymerizable resin for additivemanufacturing:

-   -   (1) 68.6% of the tri-arm oligomer prepared in Examples 4-6        above;    -   (2) 29.4% of N-methyl pyrrolidone (NMP) non-reactive diluent;        and    -   (3) 1.96% of Irgacure® 819 photoinitiator.

Example 9 Additive Manufacturing and Post-Processing

With resins prepared as described in the examples above, additivemanufacturing is carried out on a Carbon Inc. M1 or M2 apparatus,available from Carbon Inc., 1089 Mills Way, Redwood City Calif., 94063in accordance with standard techniques.

When the resin contains a non-reactive diluent, the objects canexperience a global shrinkage upon washing/extraction by the extent ofthe non-reactive diluent loading amount. Therefore, a dimensionalscaling factor is applied to the part .stl file or 3MF file to enlargethe printed part and intentionally account for subsequent shrinkageduring post processing steps.

Post processing of the produced parts can be carried out as follows:After removing the build platform from the apparatus, excess resin iswiped from flat surfaces around the objects, and the platform left onits side to drain for about 10 minutes. The objects are carefullyremoved from the platform and washed in an acetone bath for 30 secondson an orbital shaker 3 times, followed by 5 minutes of drying after eachwash. After the third wash, the parts are allowed to dry for 20 minutes,and then flood cured for 20 seconds per side, in a PRIMECURE™ultraviolet flood curing apparatus.

Next, residual non-reactive diluent (e.g. N-methyl pyrrolidone) isextracted from the parts by immersing in acetone and shaking at roomtemperature overnight. The solvent is exchanged once in the middle ofthe extraction (approximately 8 hours after start). The objects are thenremoved from the acetone and vacuum dried overnight at 60° C. The partsare then checked for residual NMP and, if no detectable residual,checked for tackiness. If the parts remain tacky, they are then floodcured under nitrogen in an LED based flood lamp (such as a PCU LED N2flood lamp, available from Dreve Group, Unna, Germany).

Examples 10-12 Preparation of a Tri-Arm MA Terminated Polyester Oligomer

These examples describe the preparation of a tri-arm, or star shaped,bioresorbable polyester oligomer. Each arm is terminated withmethacrylate. Each arm has a molecular weight of 2 kilodaltons and is ablock copolymer of poly(L-lactic acid) (PLLA) andpoly(caprolactone-r-L-lactic acid) (PCLLA) with PCLLA being the core ofthe oligomer. The PCLLA is included as 70 wt % of the total MW and theCL:L ratio is 60:40.

Example 10 PCLLA-3OH Synthesis

Refer to Table 6 for an example of the molar ratios and masses of eachreagent used for a 1 kg batch of (PLLA-b-PCLLA)-3OH synthesis as thenext two sections are discussed.

TABLE 6 Example of molar ratios and mass of each reagent needed tosynthesize a 1 kg batch of (PCL-b-PLGA)-3OH. Molecular Weight MolarDensity Mass Volume Reagent (g/mol) Ratio (g/mol) (g) (mL) MolesCaprolactone (CL) 114.14 22 1.03 418 405 3.66 Trimethylolpropane 134.071 1.08 21.4 19.8 0.16 (TMP) Stannous Octoate 405.12 2.38 × 10⁻³ 1.250.15 0.12 3.81 × 10⁻⁴ (Sn(Oct)) L-Lactide (L) 144.13 24 — 576 — 3.99

A round bottom flask was dried in a drying oven overnight and cooledunder N₂ flow to room temperature. Caprolactone, L-lactide and tinoctoate were added to the round bottom flask. The reaction flaskcontents were heated to 130° C. Meanwhile, trimethylolpropane (TMP) washeated to 130° C. Once preheated, TMP was added to the reaction flask asan initiator and was allowed to react until complete monomer conversion.Monomer conversion was monitored using H¹ NMR. The reaction was stopped,and the reaction contents were allowed to cool to room temperature. The(PCLLA)-3OH was precipitated into cold MeOH from chloroform to obtain awhite solid. H1 NMR, DSC, FTIR, and THF GPC were used to characterize(PCLLA)-3OH.

Example 11 (PLLA-b-PCLLA)-3OH Synthesis

(PCLLA)-3OH and L-lactide were added into a round-bottom flask under N₂and heated to 140° C. to melt the reaction contents. After melting, thetemperature was reduced to 120° C. and stannous octoate was added. Thereaction continued with stirring while monitoring the monomer conversionwith H¹ NMR and THF GPC. Once the reaction reached the desired molecularweight, reaction contents were cooled to room temperature, dissolved inchloroform and precipitated into cold diethyl ether three times. Theprecipitate was dried under vacuum.

Example 12 (PLLA-b-PCLLA)-3MA Synthesis

Refer to Table 7 for an example of the molar ratio and masses of eachreagent used to synthesize a 1 kg batch of (PLLA-b-PCLLA)-3MA.

(PLLA-b-PCLLA)-3OH was dissolved in anhydrous DCM in a round bottomflask under N₂. Triethylamine (TEA) and a 400 ppm BHT were added thereaction flask and the reaction flask was cooled to 0° C. in an icewater bath. The reaction flask was equipped with a pressure-equalizingaddition funnel that was charged with methacryloyl chloride. Once thereaction flask reached 0° C., methacryloyl chloride was added dropwiseover 2 hours. The reaction proceeded for 12 h at 0° C. and then 24 h atroom temperature. Once complete, the precipitate was removed via vacuumfiltration. The filtrate was collected and DCM was removed with rotaryevaporation. The resulting viscous oil was dissolved in THF andprecipitated into cold methanol. The precipitate was dissolved in DCMand washed with aqueous HCL (3%, 2 times), saturated aqueous sodiumbicarbonate solution, and saturated aqueous sodium chloride, then driedover magnesium sulfate. The magnesium sulfate was filtered off viavacuum filtration, and the filtrate was collected. DCM was removed viarotary evaporation, and the solid product was collected andcharacterized with THF GPC, H¹ NMR, FTIR, and DSC.

TABLE 7 Example of molar ratios and mass of each reagent needed tosynthesize a 1 kg batch of (PLGA-b-PCL)-3MA. Molecular Weight MolarDensity Mass Volume Reagent (g/mol) Ratio (g/mol) (g) (mL) Moles(PLLA-b-PCLLA)-3OH 6000 1 — 1000 — 0.17 Methacryloyl Chloride 104.54 4.81.07 83.6 78.2 0.80 (MC) Triethylamine (TEA) 101.19 4.8 0.726 80.9 111.50.63 Butylated hydroxy- 220.35 ~400 ppm 0.47 toluene (BHT)Dichloromethane — 0.2 g/mL — — 5000 — (DCM)

Example 13 Difunctional Oligomer Resin Formulation

The following ingredients were mixed together in the following weightpercents to provide a light polymerizable resin for additivemanufacturing:

-   -   (1) 58.82% of the difunctional oligomer prepared in Examples        10-11 above;    -   (2) 39.22% propylene carbonate (PC) non-reactive diluent; and    -   (3) 1.96% of Irgacure® 819 photoinitiator.

The foregoing is illustrative of the present invention, and is not to beconstrued as limiting thereof. The invention is defined by the followingclaims, with equivalents of the claims to be included therein.

What is claimed is:
 1. A resin useful for the additive manufacturing ofa flexible or elastic bioresorbable object, comprising or consistingessentially of: (a) from 5 or 10 percent by weight to 80 or 90 percentby weight of (meth)acrylate terminated bioresorbable polyester oligomer;(b) from 1 or 5 percent by weight to 50 or 70 percent by weight ofnon-reactive diluent; (c) from 0.1 or 0.2 percent by weight to 2 or 4percent by weight of photoinitiator; (d) optionally, from 1 or 5 percentby weight to 40 or 50 percent by weight of reactive diluent; (e)optionally, from 1 or 2 percent by weight to 40 or 50 percent by weightof filler; and (f) optionally, from 1 or 2 percent by weight to 5 or 10percent by weight of at least one additional cross-linking agent, suchas trimethylolpropane trimethacrylate (TMPTMA).
 2. The resin of claim 1,wherein said oligomer comprises a linear oligomer.
 3. The resin of claim1, wherein said oligomer comprises a branched oligomer (i.e., a staroligomer, such as a tri-arm oligomer).
 4. The resin of claim 1, whereinsaid oligomer comprises degradable ester linkages between constituentsselected from caprolactone, lactide, glycolide, trimethylene carbonate,dioxanone, and propylene fumarate monomers in an ABA block, BAB block,CBC block, BCB block, AB random composition, BC random composition,homopolymer, or any combination thereof, wherein: A=poly(lactide) (PLA),poly(glycolide) (PGA), poly(lactide-co-glycolide) (PLGA), orpolypropylene fumarate (PPF), B=polycaprolactone (PCL), polytrimethylenecarbonate (PTMC), or poly(caprolactone-co-lactide) (PCLLA), andC=polydioxanone (PDX).
 5. The resin of claim 1, wherein said oligomerhas a molecular weight (Mn) of from 2 or 5 kilodaltons to 6, 10, 15 or20 kilodaltons.
 6. The resin of claim 4, wherein said oligomer comprisesan ABA block, a BAB block, a CBC block, or a BCB block in linear and/orbranched (e.g., star or tri-arm) form.
 7. The resin of claim 6, whereinA is: (i) poly(lactide); (ii) poly(glycolide); (iii)poly(lactide-co-glycolide) containing lactide and glycolide in a molarratio of (i) from 90:10 to 55:45 lactide:glycolide (i.e., a lactide richratio) or (ii) from 45:55 to 10:90 lactide:glycolide (i.e., a glycoliderich ratio); or any combination of the foregoing.
 8. The resin of claim6, wherein B is: (i) polycaprolactone; (ii) polytrimethylene carbonate;(iii) poly(caprolactone-co-lactide) containing caprolactone and lactidein a molar ratio of 95:5 to 5:95 caprolactone:lactide; or anycombination of the foregoing.
 9. The resin of claim 4, wherein: A (PLA,PGA, PLGA, PPF, or a combination thereof) has a molecular weight (Mn) offrom 1,000 or 2,000 daltons, up to 4,000, 6,000 or 10,000 daltons); andB (PCL, PTMC, PCLLA, or a combination thereof) has a molecular weight(Mn) of from 1,000 or 1,600 daltons, up to 4,000, 6,000 or 10,000daltons.
 10. The resin of claim 1, wherein said non-reactive diluent isselected from the group consisting of dimethylformamide,dimethylacetamide, N-methyl pyrrolidone (NMP), dimethyl sulfoxide,cyclic carbonate (such as propylene carbonate), diethyl adipate, methylether ketone, ethyl alcohol, acetone, and combinations thereof.
 11. Theresin of claim 1, wherein said non-reactive diluent is propylenecarbonate.
 12. The resin of claim 1, wherein said reactive diluentcomprises an acrylate, a methacrylate, a styrene, a vinylamide, a vinylether, a vinyl ester, polymers containing any one or more of theforegoing, or a combination of two or more of the foregoing.
 13. Theresin of claim 1, further comprising at least one additional ingredientselected from: pigments, dyes, active compounds or pharmaceuticalcompounds, and detectable compounds (e.g., fluorescent, phosphorescent,radioactive), and combinations thereof.
 14. The resin of claim 1,further comprising a filler (e.g., bioresorbable polyester particles,sodium chloride particles, calcium triphosphate particles, sugarparticles).
 15. The resin of claim 1, consisting essentially of: (a)from 5 or 10 percent by weight to 80 or 90 percent by weight of a(meth)acrylate terminated, linear or branched, bioresorbable polyesteroligomer of monomers in an ABA block, a BAB block, a CBC block, or a BCBblock, wherein: A is poly(lactide) (PLA), poly(glycolide) (PGA),poly(lactide-co-glycolide) (PLGA), or a combination thereof, with saidPLGA containing lactide and glycolide in a molar ratio of either 90:10to 60:40 lactide:glycolide (i.e., a lactide rich ratio) or 40:60 to10:90 lactide:glycolide (i.e., a glycolide rich ratio), and A has amolecular weight (Mn) of from 1,000 or 2,000 daltons, up to 4,000 or10,000 daltons); B is polycaprolactone (PCL, PTMC, PCLLA) and has amolecular weight (Mn) of from 1,000 or 1,600 daltons, up to 4,000 or10,000 daltons; and C is polydioxanone (PDX) and has a molecular weight(Mn) of from 1,000 or 2,000 daltons, up to 4,000 or 10,000 daltons) and(b) from 1 or 5 percent by weight to 50 or 70 percent by weight ofpropylene carbonate; (c) from 0.1 or 0.2 percent by weight to 2 or 4percent by weight of photoinitiator, (d) optionally, from 1 or 5 percentby weight to 40 or 50 percent by weight of reactive diluent; and (e)optionally, from 1 or 2 percent by weight to 40 or 50 percent by weightof filler.
 16. The resin of claim 1, consisting essentially of: (a) from10 percent by weight to 80 percent by weight of (meth)acrylateterminated, bioresorbable, branched polyester oligomer; wherein saidbranched oligomer comprises degradable ester linkages betweenconstituents in an ABA block, BAB block, or AB random composition, whereA is poly(lactide) or poly(lactide-co-glycolide), B is polycaprolactoneor poly(caprolactone-co-lactide), and said oligomer has a molecularweight (Mn) of from 2 to 6 kilodaltons; (b) from 5 percent by weight to50 percent by weight of non-reactive diluent selected from the groupconsisting of N-methyl pyrrolidone (NMP) and propylene carbonate; (c)from 0.2 percent by weight to 2 percent by weight of photoinitiator; (d)optionally, from 1 percent by weight to 50 percent by weight of reactivediluent; (e) optionally, from 1 percent by weight to 50 percent byweight of filler; and (f) optionally, from 1 percent by weight to 10percent by weight of additional crosslinking agent.
 17. A method ofmaking a flexible or elastic bioresorbable object, comprising producingsaid object by photopolymerizing a resin of claim 1 in the shape of theobject (e.g., by additive manufacturing, such as by bottom-up ortop-down additive manufacturing).
 18. The method of claim 17, furthercomprising cleaning said object (e.g., by washing, wiping, spinning,etc.) after said producing step (but preferably before said step ofexposing said object to additional light).
 19. The method of claim 17,further comprising exposing said object to additional light after saidproducing step to further react unpolymerized constituents therein. 20.The method of claim 17, further comprising extracting residual diluentfrom said object after said producing step.
 21. The method of claim 17,further comprising drying said object (optionally but preferably under avacuum) to remove extraction solvents therefrom.
 22. The method of claim17, further comprising producing said object in enlarged form to offsetshrinkage of said object that occurs during said extracting, furtherexposing, and/or cleaning steps, and drying steps.
 23. A flexible orelastic bioresorbable object produced by the method of claim 17.